The present invention relates to a radiometer.
More particularly, the invention relates to a radiometer of the type which is already known from German published application DE-OS No. 2,639,539 and from pending German application P No. 26 39 539.1.
Still more specifically, the invention relates to an improvement in a radiometer of the type mentioned above.
Radiometers of the type known from the prior art mentioned above, are basically perfectly acceptable instruments. However, instruments of this type are subject to reproduction errors resulting from the function-dictated location of the light admitting window, and the prior art contains no teaching as to how such errors can be avoided.
The book "Das Photographische Objektiv" by Johannes Fluegge, published by Springer-Verlag, Vienna, 1955, discusses on pages 190 to 196 the Schmidt camera and the Maksutov system, both of which use the so called Schmidt mirror. The book states that aberrations can be avoided if the light admitting windows of these devices are located in the center of curvature of the mirror. These light admitting windows are aspherically deformed windows.